1. Field of the Invention
The present invention relates to a method and an apparatus for reading an image on an original, and a copying method, for the same which may be implemented in a digital or analog copying machine. More preferably, the present invention relates to a method and an apparatus for reading and copying an image on an original of large size, such as a design board.
2. Discussion of the Related Art
In a digital copying machine, an original, e.g., a document, is placed on a glass platen and pictorial information on the document is read by an image sensor of an image reading device and converted into image signals. The image signals are appropriately processed, and are outputted in the form of a reproduced picture on a copy sheet, e.g., copy paper, by means of a xerography unit or a thermal transfer unit.
Generally, in the digital copying machine, the maximum size of a document that can be read (scanned) by the machine is A3. In very large copying machines, the size is B3 at most. While it is possible to read a large document by using a large platen glass, and an optical system designed proportional to the large platen glass, this approach is impractical because the manufacturing cost is extremely large.
There has been known another image reading device that can read a document larger than the platen glass. In the image reading device, a document is moved on the platen glass by utilizing an automatic document feeder. Only thin documents can be read by such an image reading device. Large documents of 4 to 5mm thick and of A4 size, such as a design board, cannot be read by such an image reading device.